The simple answer:
FunTrivia would probably not exist in a few months from now *in any form* had I not introduced the Gold Membership functionality. Those supporting the site and paying a small subscription fee are therefore entitled to some really cool things. The checkmarks were causing system problems on the old machine so they were removed (it's machine-expensive to track, record, and display that information for tens of thousands of users a day). People requested the return of the feature in droves, so I upgraded the machine, added the support again, and added it into gold membership.
So the simple answer to your question: it simply was something that we couldn't continue to support for free. Likewise, it is quite possible that the current "you have already played this game" warnings may eventually be made gold-member only.
If you use FunTrivia so regularly and so thoroughly that you require to be warned and notificatied about quizzes that you have already played, we believe it to be more than a reasonable request that such functionality be reasonable-fee-based. While the internet may seem "free" to those who surf randomly, it simply is not for those who run the servers that make it what it is.
In the coming months I think you will find that MOST large websites will charge in some form or other.
Regards,
Terry